1. Field of the Invention
The present invention relates to an ozonizer having a first electrode and a second electrode with a discharge gap formed between them, the first electrode being covered with a dielectric.
The invention further relates to a method of manufacturing an ozonizer having two electrodes, with a discharge gap formed between them, and further with a dielectric arranged between the electrodes.
Ozonizers that serve to produce ozone operate according to the principle of silent electric discharge. An ozonizer comprises essentially two oppositely arranged electrodes, separated one from the other by a discharge gap and a dielectric. An oxygen-containing gas, such as air or pure oxygen, is directed through the discharge gap, and ozone is produced by electric discharge in the discharge gap. The electrodes are supplied with voltages of approximately 5 to 20 kV, mostly with an a.c. frequency of 50 to 60 Hz. Higher frequencies, that can be achieved by series connection of a frequency transformer, allow the ozone output to be increased.
The ozone yield of ozonizers, i.e. the ozone quantity produced per unit area, is proportional to the dielectric constant and inversely proportional to the thickness of the dielectric.
The dielectric prevents the silent discharge from changing gradually to a glow discharge or arc discharge condition, which would produce only a fraction of the ozone yield.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
EP 0 202 501 B1 discloses an ozonizer having an inner metal tube which serves as inner electrode, the metal tube being covered on its outside by a dielectric film made from a titanium oxide ceramic, sealed by a glass passivation layer. The outer electrode is provided by an outer metal tube so that the discharge gap is formed between the dielectric on the inner metal electrode and the outer metal tube.
The metal electrodes of an ozonizer of that type are exposed to heavy chemical attack by the ozone produced. In order to be able to withstand the heavy corrosive attack by the ozone, the titanium dioxide layer, with its covering glass passivation layer, must therefore be made with extraordinary care to prevent any corrosion of the covered metal tube. Further, applying a titanium oxide film and an additional passivation layer is a relatively complex and expensive process.
Another ozonizer of a similar kind has been described by EP 0 172 756 A1.
The known ozonizer comprises an inner ceramic tube, with a metallized inner surface, which is surrounded by an outer meal tube so as to form a discharge gap therebetween. In this case, the dielectric is constituted by the ceramic tube itself.
Given the fact that for technical reasons relating to the manufacturing process a minimum thickness must be observed for the ceramic tube, the ozone yield achieved with such an ozonizer is also relatively low. And in addition, to manufacture ceramic tubes with the required precision is also extraordinarily complicated and expensive.
Another ozonizer of a similar kind has been known from DE 26 18 243 C3; it comprises at least one plate-shaped or cylindrical dielectric, both sides of which are subjected to the action of an air flow, the dielectric being arranged in parallel with or concentrically between a plate-shaped or cylindrical high-voltage electrode and a plate-shaped or cylindrical grounding electrode. The dielectric consists in this case of a ceramic material with a content of 70 to 95% of aluminium oxide, less than 25% of silicon oxide and less than 10% of at least one alkali oxide or alkaline earth oxide, and has a relative dielectric constant of 5 to 10 and a thickness of 0.5 to 1 mm.
The ozone yield being proportional to the dielectric constant and inversely proportional to the thickness of the dielectric, a good ozone yield can be achieved by making the dielectric layer relatively thin and giving it a relatively high dielectric constant.
It is a problem with the known ozonizer to manufacture the plates or tubes from a ceramic material with sufficient precision; this practically can be achieved only by isostatic pressing, followed by a sintering process.
EP 0 385 177 A1 further describes an ozonizer and a method of manufacturing it, where the discharge gap is formed between to concentrically arranged metal tubes, the inner metal tube being covered by an aluminium layer, which in turn is covered by a dielectric layer consisting of several superimposed layers having different dielectric constants, the first layer adjoining the discharge gap having a lower dielectric constant than the next lower second enamel layer.
The known arrangement and the known method are connected with the disadvantage that the process of applying the different enamel layers is complicated and expensive.